1. Field of the Invention
The present invention relates to shock sensors, more specifically to shock sensors and with reed switches.
2. Description of the Related Art
Shock sensors with reed switches are known. Since these sensors are used for automobile air-bag systems, for example, they must be highly reliable.
The shock sensor with reed switches comprises a casing in which a cylindrical tube is disposed. Two reed switches are placed in the tube with an annular space formed therebetween. An insulating medium such as thermosetting resin is injected into the space for preventing the reed switches from coming into contact with each other.
Annular magnetic actuating means such as an annular magnet is disposed in one end of the annular space so as to surround one end of the tube. The actuating means is arranged to move toward and away from the contacts of the reed switches under the force of a shock and the expansion and contraction of a spring.
In the process for manufacturing the sensor with reed switches, the reed switches are positioned in the inner space of the tube so as to extend parallel to the longitudinal axis of the tube and each other. Then, the raw material of the thermosetting resin is injected into the remaining space between the inner surface of the cylindrical tube and the reed switches.
However, it is difficult to maintain the reed switches in the initial position in which they are positioned in parallel relation to the longitudinal axis of the tube and each other during the injection of the raw material of the thermosetting resin. That is, they are easily replaced during the injection.
If either reed switch comes into contact with the other or with the inner surface of the tube during the injection, the glass tube of the reed switch may be damaged or broken.
Otherwise, the reed switches may be obliquely positioned with respect to the longitudinal axis of the cylindrical tube. Shock sensors with obliquely positioned reed switches have different operation characteristics from a normal one and from each other. In other words, shock sensors in which the reed switches are obliquely positioned operate at different shock forces. This is because the distance between the first position where the magnet is initially positioned and the second position where the magnet actuates the reed switches is different among such sensors.
It is an object of the present invention to provide shock sensors with reed switches wherein the reed switches are protected from damage and breakage during the manufacturing process.
It is another object of the present invention to provide shock sensors wherein the distance between the first position where the magnetic actuating means is initially positioned and the second position where the electromagnetic actuating means actuates the reed switches, is constant thereamong.
According to one aspect of the present invention, there is provided a shock sensor comprising a casing defining a cylindrical space therein, a protecting tube placed the cylindrical space so as to define an annular space between the casing and the protecting tube and having an inner space therein, a partitioning member provided in the inner space so as to extend parallel to the longitudinal axis of the protecting tube and to divide the inner space into a plurality of compartments extending substantially parallel to the protecting tube, a plurality of reed switches positioned one in each of the compartments, insulating members placed in remaining spaces in the compartments, and a magnetic actuating device provided in the annular space around the protecting tube for actuating the reed switches when a shock of predetermined magnitude acts on the sensor.
According to the first aspect of the present invention, the raw material for the insulating member is injected with the reed switches separately positioned in each of the compartments divided by the partitioning member. Therefore, the reed switches do not contact each other during injection. Accordingly, scratching or damaging of the closed glass tubes of the reed switches by contact therebetween is prevented to increase the production yield.
Further, according to the first aspect of the present invention, since each reed switch is positioned in a compartment extending substantially parallel to the longitudinal axis of the protecting tube along which the electrical actuating means moves, it is not significantly obliquely positioned during the injection of the raw material for the insulating member. Therefore, the operating characteristics become constant among a plurality of the sensors.
In the above shock sensor, the partitioning member may be a partitioning plate which divides the smaller space into two compartments and extends at a central portion of the inner space.
In the above shock sensor, the two compartments may be completely separated by the partitioning plate.
In the shock sensor thus constructed, the reed switches can be completely separated.
In the above shock sensor, the partitioning plate may be separately formed from the protecting tube.
According to the above shock sensor, the partitioning plate may integrally formed with the protecting tube.
In the shock sensor thus constructed, the number of the elements can be reduced and no step is needed for mounting the partitioning plate in the protecting tube.
In the above shock sensor, the partitioning member may include an opening fluidly connecting at least two of the compartments with each other.
In the shock sensor thus constructed, flowable raw material injected into one of the compartments can flow into the other compartment through the opening in the injecting operation. Since the injecting operation can therefore be completed by injection to one of the compartments, the productivity of the sensor is increased.
In the above shock sensor, the insulating members may be made of thermosetting resin.
In the above shock sensor, the opening may be located at one end of the partitioning plate.
According the another aspect of the present invention, there is provided a shock sensor comprising a casing defining a cylindrical space therein, a protecting device placed in the cylindrical space so as to define an annular space between the casing and the protecting device and having at least one elongated cylindrical space extending in parallel with the longitudinal axis of the protecting device, at least one reed switch received in the elongated space, and a magnetic actuating device provided in the annular space around the protecting tube for actuating the reed switch when a shock of predetermined magnitude acts on the sensor.
According to the second aspect of the present invention, since the reed switch is positioned in the compartment extending substantially parallel to the longitudinal axis of the protecting device, it is not significantly obliquely positioned during the injection of the raw material for the insulating member. Therefore, the operating characteristics become constant among a plurality of the sensors.
In the above shock sensor, an inner diameter of the elongate cylindrical space is slightly larger than an outer diameter of the reed switch.
In the shock sensor thus constructed, the reed switch is not obliquely positioned during the injection of the raw material for the insulating member. Therefore, the operating characteristics become constant among a plurality of the sensors.
In the above shock sensor, an insulating member may be provided between the reed switch and the protecting device.
In the above shock sensor, the insulating member may be made of thermosetting resin.
In the above shock sensor, the protecting device may comprise a protecting tube and a protecting member placed in the protecting tube and the elongated cylindrical space be formed in the protecting member.
In the above shock sensor, a plurality of the elongated cylindrical spaces may be formed in the protecting member.
In the above shock sensor, at least two of the elongated cylindrical spaces may be fluidly connected by a passage means.
In the shock sensor thus constructed, flowable raw material injected into one of the cylindrical spaces can flow into the other cylindrical space through the passage means in the injecting operation. Since the injecting operation can therefore be completed by injection to one of the cylindrical spaces, the productivity of the sensor is increased.
In the above shock sensor, an auxiliary recess for receiving a lead wire may be formed in the insulating member so as to extend along the elongated cylindrical space.